The present invention relates to a contact detecting device having a cord-shaped pressure sensitive sensor provided on a contact detecting object and serving to accurately and rapidly detect that a part of a thing or a human body comes in contact with the contact detecting object with a pulse output obtained by applying force to the cord-shaped pressure sensitive sensor, and a vehicle comprising the contact detecting device.
Conventionally, a contact detecting device of this type and a running device have detected a contact with an obstacle by means of a bumper sensor comprising a tape switch (for example, see Japanese Patent Document JP-A-8-58501.
FIGS. 10A and 10B are views showing a running device comprising a conventional contact detecting device described in the Patent Document 1, FIG. 10A being a schematic view showing a side surface and FIG. 10B being a schematic view showing a planar section.
In FIGS. 10A and 10B, 80 denotes a running device, 81 denotes a running device body, 82 denotes a truck, 83 denotes a driving wheel, 84 denotes a driven wheel, 84a denotes a front driven wheel and 84b denotes a rear driven wheel. 85 denotes a bumper. 86 denotes a bumper sensor comprising a tape switch. Thus, the conventional contact detecting device has such a structure that the tape switch 86 is provided around the bumper 85. When an obstacle comes in contact with the bumper 85 while the running device 80 is running, the tape switch of the bumper sensor 86 is turned ON so that the contact of the obstacle is detected. When the bumper sensor 86 detects the contact of the obstacle, the driving operation of the driving wheel 83 is stopped.
Moreover, since the bumper sensor 86 is the tape switch, it is turned ON if a small rounded portion is present in a provision portion. As shown in the drawing, therefore, it is necessary to form an insertion hole 85b inserting the bumper sensor 86 on both sides of a corner section 85a of the bumper 85 and to provide the bumper sensor 86 excluding the small rounded portion such as the corner section 85a. 
With the structures of the conventional contact detecting device and the conventional running device, however, the insertion hole 85b inserting the bumper sensor 86 is provided on both sides of the corner section 85a, and furthermore, the bumper sensor 86 is to be inserted therein. For this reason, there is a problem in that a great deal of time and labor is taken and the hole is made to give a poor appearance.
In order to previously solve the problem, therefore, it is provided a cord-shaped pressure sensitive sensor around a bumper, thereby eliminating the necessity for forming an insertion hole on both sides of a corner section.
Description will be briefly given to the reason why an ON state is not brought even if the cord-shaped pressure sensitive sensor is bent and provided in the corner section of a bumper perpendicularly.
The cord-shaped pressure sensitive sensor is a cable-shaped sensor using a piezoelement material, and FIG. 1 shows a structure thereof. In FIG. 1, 10 denotes a cord-shaped pressure sensitive sensor in which a core (a center electrode) 1 is provided on a center in an axial direction and the center electrode 1 is covered with a piezoelement material 2, and furthermore, a ground electrode 3 is provided around the piezoelement material 2 and an outermost periphery is covered with a PVC (vinyl chloride resin) 4.
The cord-shaped pressure sensitive sensor 10 uses, for the piezoelement material 2, a resin-based material having a heat resistance which was developed originally by the applicant and has a working temperature of 120° C. or less, and can be used in a higher temperature region (120° C. or less) than 90° C. to be a maximum working temperature of a polymer piezoelement material (uniaxial drawn polyvinylidene fluoride) and a piezoelement material (a piezoelement material of chloroprene and piezoelectric ceramic powder) which are conventionally typical. The piezoelement material 2 is constituted by a resin having a flexibility and piezoelectric ceramic, and furthermore, is constituted by using a flexible electrode comprising a coil-shaped metallic center electrode and a film-shaped ground electrode and has a flexibility which is equivalent to that of an ordinary vinyl cord.
Furthermore, the cord-shaped pressure sensitive sensor 10 has a high sensitivity which is equivalent to that of the polymer piezoelement material, and has a high sensitivity which is equivalent to that of the polymer piezoelement material in such a low frequency region (10 Hz or less) as to detect the pinching of a human body. The reason is that the dielectric constant (approximately 55) of the piezoelement material 2 is greater than that (approximately 10) of the polymer piezoelement material and a reduction in the sensitivity is therefore small also in the low frequency region (10 Hz or less).
The piezoelement material 2 is constituted by a complex including a resin-based material and piezoelectric ceramic powder having a size of 10 μm or less, and an oscillation detecting characteristic can be realized by ceramic and a flexibility can be realized by a resin. The piezoelement material 2 can realize a high heat resistance (120° C.) and a flexibility which can easily be obtained by compounding an amorphous polyethylene based resin (a molecular weight of approximately 300,000) and an amorphous polyethylene based resin (a molecular weight of approximately 100,000) as a resin based-material, and can carry out a simple manufacturing process which does not require bridging.
The cord-shaped pressure sensitive sensor 10 thus obtained has no piezoelectric performance with the piezoelement material 2 molded. By applying a high DC voltage of several kV/mm to the piezoelement material 2, therefore, it is necessary to carry out a processing (a polarization processing) of giving the piezoelectric performance to the piezoelement material 2. The polarization processing is carried out by forming the center electrode 1 and the ground electrode 3 on the piezoelement material 2 and then applying a high DC voltage to both of the electrodes. In the case in which a very small defect such as a crack is present in the piezoelement material 2, a discharge is carried out in the defect portion so that both of the electrodes are apt to be short-circuited. Consequently, a sufficient polarization voltage cannot be applied. In the invention, however, an original polarizing step using an auxiliary electrode capable of adhering to the piezoelement material 2 having a constant length is established so that a defect can be detected and avoided to stabilize polarization. Consequently, an increase in a length of several tens meters or more can also be implemented.
In the cord-shaped pressure sensitive sensor, moreover, a coil-shaped metallic center electrode is used for the center electrode 1 and a film-shaped electrode (a three-layer laminated film comprising aluminum—polyethylene terephthalate—aluminum) is used for the ground electrode 3. Consequently, the adhesion of the piezoelement material 2 and the electrode can be maintained and the connection of an external lead wire can easily be carried out so that a flexible cable-shaped mounting structure can be obtained.
The center electrode 1 is formed of a copper—silver alloy coil, the ground electrode 3 is formed of the three-layer laminated film comprising aluminum-polyethylene terephthalate—aluminum, the piezoelement material 2 is formed of a polyethylene based resin and piezoelectric ceramic powder, and a housing is formed of thermoplastic. Consequently, a dielectric constant is 55, an electric charge generation amount is 10 to 13 C (coulomb)/gf, and a maximum working temperature is 120° C.
FIGS. 2A and 2B are charts showing a load applied to the cord-shaped pressure sensitive sensor 10 and a sensor output characteristic. The applicant conducted an experiment on the relationship between the load of the cord-shaped pressure sensitive sensor 10 and the sensor output. As a result, when a bending load shown in FIG. 2A is applied to the cord-shaped pressure sensitive sensor 10, the sensor output presents a phenomenon shown in FIG. 2B.    (1) More specifically, when the load is not applied to the cord-shaped pressure sensitive sensor 10 at a time t0, the sensor output indicates 2(V).    (2) When a bending load is applied to the cord-shaped pressure sensitive sensor 10 in a constant direction at a time t1, the sensor output is increased to 4(V) the moment the bending load is applied and is then inverted to 0(V) immediately, and is thereafter returned to 2(V) again.    (3) Subsequently, the sensor output is maintained to be 2(V) with bending.    (4) When the cord-shaped pressure sensitive sensor 10 is returned to an original state at a time t3, the sensor output is decreased to 0.8(V) instantaneously and is then inverted to 2.2(V) immediately, and is thereafter returned to 2(V) again.
In the cord-shaped pressure sensitive sensor, thus, a signal is output only the moment force is applied. Even if the force is then applied continuously, an output is not sent any longer until a fluctuation is generated. Similarly, the cord-shaped pressure sensitive sensor has such a characteristic that the output is sent the moment the force is removed. Also in the case in which the cord-shaped pressure sensitive sensor is bent and provided perpendicularly in the corner section of a bumper, accordingly, it is brought into an ON state the moment it is bent, and the output is not sent after the completion of the provision. Then, the output is sent when force is applied to any part of the cord-shaped pressure sensitive sensor.
If the cord-shaped pressure sensitive sensor is provided around the bumper, thus, it is not necessary to provide an insertion hole on both sides of the corner section.
FIGS. 3A and 3B are view showing a running device having the cord-shaped pressure sensitive sensor provided around a bumper, FIG. 3A being a schematic view showing a side surface and FIG. 3B being a schematic view showing a planar section.
In FIG. 3A, 20 denotes a running device, 21 denotes a running device body, 22 denotes a truck, 23 denotes a pair of left and right driving wheels, 23a denotes a motor for driving the wheels, 24 denotes a driven wheel, 24a denotes a front driven wheel and 24b denotes a rear driven wheel. Moreover, 25 denotes a bumper and 26 denotes a bumper sensor unit. The cord-shaped pressure sensitive sensor 10 (FIG. 1) is provided in the bumper sensor unit 26.
In FIG. 3B, furthermore, 27 denotes contact detecting means for detecting an output from the cord-shaped pressure sensitive sensor 10, and 28 denotes driving control means of the motor 23a for driving the pair of left and right driving wheels 23.
FIG. 4A is a block diagram showing the contact detecting means 27 in FIG. 3.
In FIG. 4A, the contact detecting means 27 comprises a contact detecting section 27b for detecting the contact of an obstacle based on the output signal of the cord-shaped pressure sensitive sensor 10 upon receipt of the same signal. A signal output from the contact detecting section 27b is given to the driving control means 28, and the driving control means 28 immediately stops the motor 23a upon receipt of the same signal, thereby stopping the driving operation of the pair of left and right driving wheels 23.
Thus, the contact detecting device 27 is constituted by the bumper sensor unit 26 including the cord-shaped pressure sensitive sensor 10 and the contact detecting means 27. The bumper sensor unit 26 is attached to the bumper 25 provided around the running device body 21 as shown in FIG. 5A.
FIGS. 5A and 5B are enlarged sectional views showing a bumper sensor unit to be a contact detecting device attached to a bumper, and FIG. 5A is a sectional view taken along an A—A line in FIG. 3B. FIG. 5B is a sectional view showing a bumper sensor unit according to the invention which will be described below.
In FIG. 5A, the bumper sensor unit 26 shown in FIG. 3 is constituted by an elastic fixing member 30 to be fixed to the bumper 25 through a fixing plate 38 with a fixing screw 39, and the cord-shaped pressure sensitive sensor 10 shown in FIG. 1 which is provided in the elastic fixing member 30.
The cord-shaped pressure sensitive sensor 10 is obtained by coaxially molding the center electrode 1, the piezoelement material 2 and the ground electrode 3 as described with reference to FIG. 1. A piezoelement material comprising a mixture of a resin based material and piezoelectric ceramics powder is used for the piezoelement material 2, and the piezoelement material 2 has a flexibility as a whole sensor.
On the other hand, the elastic fixing member 30 is formed by using rubber or thermoplastic elastomer including a space for accommodating the cord-shaped pressure sensitive sensor 10, a gap section 32 for accommodating the fixing plate 38, and a hollow section 35 for forming an elasticity. The hollow section 35 has a rib 31 for maintaining shapes provided on a center in such a manner that the elastic fixing member 30 is neither deformed by a dead weight nor crushed by a corner section 25a of the running device body 21. In the elastic fixing member 30, the fixing plate 38 is inserted in the gap section 32 and is secured to the bumper 25 with the screw 39 in a cantilever condition. When the cord-shaped pressure sensitive sensor 10 is to be provided in the elastic fixing member 30, it is preferable that a tongue section 33 should be turned up and a slit section 34 should be opened to slide and put in the cord-shaped pressure sensitive sensor 10.
Moreover, it is preferable that a dimension L in a height direction of the elastic fixing member 30 should be set to be greater than a distance at which the running device runs while the contact detecting means 27 detects a contact with an obstacle and the control means 28 then controls the stop of running.
By the structure described above, the running device 20 outputs a signal to the contact detecting means 27 when the cord-shaped pressure sensitive sensor 10 provided around the bumper 25 senses a contact, and the contact detecting means 27 decides the contact of the obstacle based on the same signal to send an output signal from the contact detecting section 27b to the driving control means 28, and the driving control means 28 stops the motor 23a immediately upon receipt of the same signal, thereby stopping the driving operation of the pair of left and right driving wheels 23. Consequently, the running device 20 is stopped while the elastic fixing member 30 is deformed. Thus, the bumper 25 can be prevented from colliding with the obstacle. Thus, the running device is safely used as an automated guided vehicle when a baggage is to be carried automatically.
By using the cord-shaped pressure sensitive sensor 10 (FIG. 1) in place of the bumper sensor comprising the tape switch described in the Patent Document 1, thus, a signal is output only the moment force is applied and the output is not sent any longer until a fluctuation is caused even if the force is then applied continuously. Consequently, it is possible to produce a great advantage that the insertion hole does not need to be provided on both sides of the corner section of the bumper.
However, since the cord-shaped pressure sensitive sensor has an excessively high sensitivity, it reacts to a fine oscillation during the running operation of the running device in some cases. Moreover, there is a problem in that the pressure sensitive sensor reacts to a great impact generated when the running device runs on a step, and erroneously detects the impact.
The erroneous detection is rather desirable in respect of fail-safe, and is not preferable in respect of a workability when stopping is carried out without a contact.